chemical physics of discharges - Argonne National Laboratory

234
The Plasma Induced Reaction of Hydrogen Sulfide with Hydrocarbons
F. J. Vastola and W. 0. Stacy
Department of Fuel Science
The Pennsylvania State University, University Park, Pa.
Introduction I
The interaction of sulfur with hydrocarbons under a range of experimental
conditions has been investigated by various workers. Knight and co-workers1 re-
acted excited sulfur atoms, produced by 'in situ' photolysis of COS at 25OoC, with
a range of paraffinic hydrocarbons and found as primary products only the corre-
ponding mercaptans. Bryce and Hinsnelwood2 studied the reaction of sulfur vapor
with parafinnic hydrocarbons in the temperature range 320°C to 349°C and observed
that the primary products were hydrogen sulfide and unsaturated hydrocarbons.
Study of the reaction of sulfur and methane 3-7 over a catalyst at 500°C to 7OO0C
has shown the products to be carbon disulfide and hydrogen sulfide according to
the reaction
CH4 + 2S2 -+ CS 2 + 2H2S. (1)
Thomas and Strickland-Constable8 studied the interaction of sulfur and hydrocarbons
at temperatures 1200.OK to 1500'K and in the absence of a catalyst observed no carbon
disulfide formation. With a catalyst, however, the reaction proceeded yielding
carbon disulfide, hydrogen sulfide, and hydrogen; reactions similar to (1) for
methane, above 1200°K, being increasingly superseded by those similar to (2):
CH4 + S + CS2 + 2H2*
2
Reported now are some results of a study of the reactions of excited atomic
species, generated by the dissociation of hydrogen sulfide in a plasma jet, with
methane and neopentane.
9
This study was suggested by an earlier investigation of Vastola and co-workers
into the reaction between carbon and the products of water vapor microwave discharge,
where it was observed that the presence of carbon downstream inhibited the recom-
bination, to either oxygen or water, of the active atomic species. Instead, the
active oxygen reacted preferentially with carbon.
Experimental Procedure
The plasma reactor is shown in Figure 1. The reactor consists of a 10 x 0.75
inch fused quartz tube. The gas to be brought to the plasma state is introduced
tangentially upstream from the output coil of a 1.2 KW, 120 MHz RF induction heater.
Ihe spiraling motion imparted by the tangential input increases the dwell time of
the gas in the plasma zone. The hydrocarbon gases to be reacted with the plasma
dissociation products are introduced down stream from the plasma flame.
By moving
the hydrocarbon feed tube the distance between the plasma flame and the point of
hydrocarbon introduction can be varied.
TO initiate the plasma discharge argon is passed through the reactor (0.5 CU
ft/hr, 1 Atm) and a graphite rod is placed in the induction field. After the heated
graphite rod starts the discharge it is removed and the gas feed is switched to the
desired H2S-Ar mixture. Mass spectrometric gas analyses were made before and after
the reaction.
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